This invention relates to electronic devices and systems for automatically controlling the relative levels of multiple audio signal sources, particularly from microphones used by different participants in a meeting, performance or the like, and for controlling the underlying background noise signal (ambiance).
There is an ongoing effort to improve the performance of automatic level control and audio mixer systems for multiple microphone channels so as to minimize feedback from loudspeakers that causes mic "squeal", and unnecessary amplification of background noise (ambiance) as the number of mics in use varies. In a typical automatic mic mixing installation, two or more program microphones may be placed in different locations in a auditorium or meeting room for use by the participants. A background pick-up (ambiance microphone) may be placed at a location away from the speakers and from other direct sound sources for gathering indirect background noise. A level controller, which may also include a mixer, receives these various microphone inputs and attempts to automatically establish relative gain levels that adjust to the number of active (open) program microphones. The gain in the individual program microphone channels and the ambiance level are relatively increased and decreased in response to microphone usage so that the participants or performers are heard without unnatural or unpleasant modulation of the program sources, such as the speaker's voices, or of the noise level, and without allowing the overall system gain to reach a point where feedback oscillations cause "squeal".
A number of systems have been conceived and developed with these general or similar objectives in mind. The following list of prior patents of more recent design are cited as representative: U.S. Pat. No. 3,992,584 (Dugan); U.S. Pat. No. 4,149,032 (Peters); U.S. Pat. No. 4,374,300 (Panto); U.S. Pat. No. 4,489,442 (Anderson); and U.S. Pat. No. 4,864,627 (Dugan).
The foregoing prior systems and others previously proposed have various advantages over a signal combining system in which the levels of the background and program microphones are unprocessed and summed without relative gain adjustment. However, the prior systems have various drawbacks that this invention overcomes in providing a novel and more reliable automatic mixing system that is less costly to manufacture and service than has been afforded by prior systems.